Transducer



w. T. HARRIS TRANSDUQER FlG. l.

March s, 1959 Filed Del. so, 1954 Alvi TRANSDUCER Wilbur T. Harris, Southbury, IConn., assignor to The lHarris Transducer Corporation, Woodbury, Conn., a

corporation of Connecticut Application December 30, 1954, Serial No. 478,837 zo claims. J (c1. 340-11) My invention relates to an electromechanical transducer and, in particular, to a construction adapted for underwater use primarily in the audio-frequency range.

Radially vibrating cylindrical transducers of the magneto-strictive type may be designed from either one of two distinctly different viewpoints, yielding two classes of transducers having distinct and contrasting properties. While the differences appear at first to be differences in degree, they seem fundamental and marked to such an extent that they should be regarded as differences in kind. For identification, these basic varieties can be called the thick-wall and the thin-wall types, or Type I and Type II, respectively.

Type I (thick wall) is well known. It is moderately etlicient at its resonant frequency, but is normally very poorat one fourth of an octave away from this frequency. Here efficiency is dependent on at least a moderately high mechanical Q, and increases with the wall thickness of the cylinder, which for a magnetostrictive case is assumed to be laminated.

Type Il (thin wall) has a very low mechanical Q in water, and operates mainly in the broad frequency region below resonance, the stiffness-controlled frequency region. Efficiency increases -asthe wall is made thinner, in direct contrast to Type I. There is no sharp eiciency peak at resonance, but only a broad smooth eiciency maximum, since Q is only in the order of l.

' The yresonant frequency, or frequency of maximum eciency, is generally about three times lower for transclucers of Type II than for transducers of Type I of the same diameter. Thus, for low-frequency use, the Type Il cylinder is .about one third the diameter, and perhaps one thirtieth the weight, of the Type I cylinder. Because of its reduced size, the energy density which Type II can handle is necessarily reduced, but not necessarily the efficiency. Therefore, since (for low-frequency sonar arrays) large surface area is necessary for the sake of directivity, the power-processing capacity of Type II trlansducers may be adequate in highly directional assemles.

The behaviours and distinctions of the two basic transducer types-can be understood in terms of the following equation:

F 1mm-IT".-

2,876,427 Patented Mar. 3 1959 faice the reactive terms in the impedance (the denominator of the expression) is always large compared to the total of the resistance terms. However, at one frequency, namely, resonace (wo), the reactive terms are equal and opposite in sign, and hence cancel. At this frequency, the velocity is determined by the resistance only, and a sharp maximum in efficiency occurs. If the resistance is largely radiative (acoustic), the eiciency will be high at this frequency. At other frequencies, the mechanical reactance is so high that the device cannot be made to respond signicantly, land in practice the eiliciency is very low. When very high force'is required to produce significant velocity (i. e. off resonance), electrical dissipation, which is not explicitly shown in the force term, consumes a large part of the input power.

In the Type II (thin-walled, broad-band) transducer, the stiffnessand mass-reactive terms are both small, in the same order of magnitude as the resistive terms; hence, when the reactive terms cancel at resonance, no prominent resonant peak occurs. If, therefore, the RA term can be made to dominate, and force can be exerted with only small electrical losses, the result is broad-band high-efliciency performance. Etlicient broad-band performance is often far preferable to equal efficiency in a narrow band. Furthermore, a broad-band transducer having an eiciency maximum at a given frequency is generally about one third the diameter of a narrow-band transducer having its efficiency maximum at the same frequency, as previously noted.

In spite of the various considerations expressed above with regard to properties of Type I and Type II cylindrical transducers, substantial problems of size and weight are encountered (whether Type I or Type Il) when attempting to achieve directional performance with array configurations. The inherently omnidirectional property of each transducer element means that, when combined in an array to achieve directional properties, there is considerable excess bulk, and the power-toweight ratio suffers.

It is, accordingly, an object of the invention to provide an improved transducer construction of the character indicated.

.It is another object to provide a new transducer ele'- rnent construction, particularly adapted to plural com bination in arrays to achieve directional properties.

It is also an object to meet the above objects with a device characterized` by high e'lciency and power-handling capacity when used as a transmitter and also by good performance and reception when used merely as a hydrophone.

It is still another object to provide a new type of transducer construction achieving many of the advantages of radially strictive cylindrical transducers and, at the same time, characterized primarily by a unidirectional rather than an omnidirectional response.

It is a general object to meet the above objects with a basically rugged structure presenting relatively few constructional problems, and inherently achieving a directional response with a good power-to-weight ratio.

Other objects and various further features of novelty and invention will be pointed out or will occur to those skilled in the art from a reading of the following specification in conjunction with the accompanying drawings. In said drawings, which show, for illustrative purposes only, preferred embodiments of the invention:

Fig. l is a perspective view of a transducer element incorporating features of my invention and partly broken away to reveal internal structural features; and

Fig. 2 is a perspective view of an array utilizing elements, as of the type shown in Fig. 1, to achieve desirable directional properties.

Briey stated, my invention contemplates a basically new type of transducer construction, whereby the high eciency and power-handling capacity of the ordinarily omnidirectional radially strictive cylindrical transducer is achievable with -a predominantly directional response and with a saving in spaceorvolume requirements. :Basically, my improved transducer utilizes an arcuate segment of a cylindrical transducer of `one of kthe ,abovediscussed general types. The generalprinciple is applicable to any radially `strictive device, such as barium titanate or the like, but, in the form specifically `disclosed herein, magnetostrictive effects are utilized, and therefore a complete `return path is required fork circulation of magnetic ux. Because of 4its overall ,cross-section appearance, `I call my construction a .new-rnoon transducer,

.In themagnetostrictive variety ofinew-moon transducer, the return flux is passed vdirectly between the limits of the cylindricalarc 'of the transducer and may `extend ,directly lchordally `of these limits. Both the arc and the chord must of course be of flux-conducting material, and I `prefer that one of these parts shall be magnetostrictive while the other exhibits a relatively non-magnetostrictive effect; in the specific form disclosed, the arc is magnetostrictive andthe chord is of relatively non-magnetostrictive material, such as silicon steel, which, to reduce eddycurrent losses, may be a stack of silicon-steel laminations. The transducer is completed by providing means for magnetizing the `llux rpath and a signal winding for electromagnetic coupling; the magnetizing means may be andpreferably is apermanent magnet, as of iron-oxide ceramic known as ferrite. Certain details of construction of the elemental `device to be described render the same adaptable to use `in multiple-element arrays, anda specitic array is also disclosed.

Referring to Fig. yl of the drawings, my invention ris' shown in application lto `a basic Vnew-moon `transducer element, comprising essentially an elongatedcylindrically arcuate radially strictive element 10, kwhich may comprise a plurality of laminations of magnetostrictive.material, such as nickel, bonded `to eachother to form asinglepiece arc. The tlux path may be considered (for any cross section of the device) to include the arcuate part and a return path of linx-conducting material; an L,

arcuate pressure-release layer 9, as of corkCorprene, or the like, is positioned .behind the arcuate part 10. As

-indicated generally ifabove, 1vthe :return path `may Lextend directly lchordally'of the `limits 1 of theA arc V10; in the'form shown, the chord portion comprises two dat stacks 11-12 of laminations of .as-material exhibiting .relatively low magnetostrictive-eiect, such as silicon steel. The laminations may be grooved, as-at 13, to `accommodate inserted 'ends of the arc 10, for firm and positive anchorage thereof.

Magnetizing means may vcomprisea magnetizing winding linked to thedescribed viiuxpath, but I indicatemy preference for a permanentmagnet 14 which may be inserted between the stacks-11-12 to form a part of the return path. The permanent magnet 14 is preferably a `single block oria longitudinal succession of blocks of `suitably formed iron-oxide ceramic, known as va ferrite, and bonded at both lateral extremities to therespective stacks 11-12 of -return-pathllaminations.

The basic new-moon ele'ment construction further includes a signal winding 1S-"enveloping theflux -path dened by the chord anda'rcfand it-is convenient' to apply the lsignal winding lonly over -the arc-portion `10 (as shown).

To provide a solid base for the elemental construction described, I show :a base-plate 16-ofnon-magnetic mate- `rial, such as aluminumytheplate 16 being coextensive with the chordal return path `11--12---14 and with the `longitudinal axis l'or `extent fof theentire transducer. A 'variety o'f methodsmay be 'fernployed for securingthe base plate 16 to the elements-ofthe return"path,but`-I merely suggest, at `the layer 17, the application of a su'flicient thickness of phenolic or other vinsulating and bonding agent, to provide an extensive area of firmly bonded support and to avoid short-circuits between laminations. For the sake of clarity at the front or left end in the drawing, the inner volume 18 of the transducer is shown open and unfilled, butfpreferably this inner volume is completely and intimately lledwith sound-transmitting material, such as plastic pottingk (suggested at 18'), which may not only ll the space Vwithin Athe transducer but "also coat and thoroughly bond `and support and coverall externally exposed portions ofthe described parts.

Tocornplete the assembly, a lead cable 19mm/beprovided at one end, and a protective boot of sound-transmitting rubber or Arubber-like material '20 may completely and intimately encase the potted device. For mounting purposes, it is convenient to provide integral resilient ,ilanges, as at :21, projecting integrally Aoutfrom the limits of the chord and ,ar,c,;and substantially coextensivewith the longitudinal dimension `of the transducer. Mounting holes, as at `22,rnay be ,providedxat intervals along Athe `longitudinal dimension `of the flanges ,21, -and Lprefer 4that the flanges 21, particularly in .the vicinity of `the mounting holes 22.be internally reinforced, as suggested at 23 and as described `in,greater,detaillinxmy copending patent application Serial No. 454,712, ztiled lSeptember 8, 1954.

In operation, it will bettseen that, for fthe ,case oa magnetostrictive arc ,10 zand of a relatively non-magnetostrictive chord 11--12-14, the,basicorganization'of :my transducerY is :i analogous '.to :a `bow ot' `variable Varcuate tex- -tent, with lixedly anchored ends. For the esituation tin which the chord ismagnetostrictve and the arc 10 isrelativelynon-magnetostrictive, the system .is analogous .to a bow of `fixed arcuate extentflbut having ends which are f -variably spread. .In either Aevent, the :action is such, by

virtue of the limited arcuate extent v(i. e. lessi-,than 180) of the arc, r.that greater radial displacements occur :for the central portion `of the arc than could be `achieved :for an arc of 180 :or for a fully cylindrical magnetostrictive core. Moreimportantly, the radial `displacements 4are directionally confined, so that' the organization lends itself particularly to array configurations.

It will be understood that it istall the-,samefwhetherfthe arcuate portion 10 is stated :to be `less ,than '180 or whether `the chord portion 11-- 12-,14 isstated ;to.be less than twice lthe reifectiveiradius of the chord; portion 10. The latterfexpressionimay, howevergserve ptomake above, characterizedas itlis 'by elastic deformation @ofthe arc vportion '10throughsmechanical reaction betweentthe arc and chord :portions of t the'core, `in ,the context of; the `geometry shown and set` forth. I1 he actual y,displacements achieved at thezceutralzpart-of` the :arc 10 =exceed `those attributable solely tormagnetostrictive action,` all :because of the described 4dissimilarity of `core .materials .and :because of the chord-arc geometry, as will be understood.

IAs indicated, the 1' elemental s new-moon :transducer of Fig. 1 may bereadilyladapted:inmultipleftozthe.construcrelatively :little response will be exhibited in the aback direction. In order to minimize y,this .backresponsein the fformtshown, It provide ,a diaphragmmemberA 33 ;ionwhich are supported a plurality of transversely extending rod or bar-type damping devices 34; these bars may be of suitably loaded rubber or rubber-like material bonded to the plate or diaphragm 33, and I indicate my preference for rubber bars 34 loaded with aluminum pellets. In addition to damping means 34 to minimize back response, I also show a reflecting channel 35 containing compliant material, such as air-cell rubber. The panel 35 may be a single assembly serving the entire transducer array and of the construction described in greater detail in my copending patent application Serial No. 426,219, tiled April 28, 1954, now Patent No. 2,811,216.

In order to supportv the rellecting panel 35 and the damping assembly 33-34 in uncoupled relation, I have shown rubber or rubber-like side members 36 connecting the support means for the panel 35 to the support means for the diaphragm 33; in each case, angle members 37-38 suffice to provide connection to the rubber side member 36. When the electrical interconnections between newmoon elements 25-28 have been established and sealed, the device of Fig. 2 as described is inherently rugged enough to withstand mounting and use without further protection. However, for appearance sake, and to provide against direct fouling of the transducer element, the described assembly may be mounted within a freeiiooded dome of known construction, b'ut no particular precautions need be taken within the dome to reduce back response. t t ,t y

The new-moon transducer shown in the drawings may be viewed as Type II, or the thin-walled, broad-band type, and it is advantageous for lower audio frequencies especially. Its advantages appear from the following comparative consideration of corresponding fully cylindrical elements. A lkc. (maximum efiiciency), Type-I, cylindrical (resonant) magnetostrictive transducer would have a diameter of about 5 feet, while a corresponding Type-II transducer would have a diameter of about 20 inches. The S-foot diameter (Type l) is totally unsuited for array use, and the 20-inch diameter Type Il is undesirably large. On the other hand, the new-moon adaptation of the Type II, as shown in Fig. l, and employing a segment of a 20-inch diameter cylinder (with a planar laminatedsilicon-steel, magnetic-return circuit), is relatively thin and of lesser transverse dimension, so that an array as in Fig. 2 can make a compact wall of transducer radiating surface.

Besides its compactness and convenience for use in arrays, my new-moon construction is ideally adapted to the use of permanent magnets (14) in the magnetic circuit, to make the unit immune to depolarization when energized at high power levels. Further, it is ideally adapted to use in unidirectional arrays, and to building into balile structures which shield the transducers on the back or flat side.

It will be seen that I have described a novel transducer construction lending itself particularly to directional respouse and yet possessing the inherent advantages of the otherwise unidirectional, radially-strictive, cylindrical transducer. The basic construction is so versatile that it may be designed for narrowor broad-band performance and is not limited as to applicability in the lower audio range; however, in the lower audio range, the permanent-polarization feature permits making maximum use of the active material and achieves a high power-toweight ratio. Generally speaking, for relatively narrowband applications (Type I), it is desirable to design the arcuate member with a ratio of radius-of-curvature to wall-thickness of about 5:1, whereas, for broad-band applications (Type Il), the ratio is more in the order of 50:1. Aside from inherent broad-band characteristics, and` greatly reduced size and weight of individual elements, the Type II new-moon transducer is ordinarily preferred for low-frequency applications because of lts superior efciency, due to low eddy-current losses inherent in the construction.

6 While =I have described 'the invention in detail for the preferred form shown, it will be understood that modifications may be made within the scope of the invention as delined in the claims which follow.

I claim:

l. A transducer comprising a cylindrical arc of radially strictive material, said arc being of extent less than means electrically responsive to radially strictive action of said material, and relatively heavy backing-plate means relatively rigidly connecting the arcuate limits of lsaid radially strictive material.

2. Artransducer comprising a cylindrical arc of radially strictive material, means electrically responsive to radially strictive action of said material, means relatively rigidly connecting the arcuate limits of said radially strictive material, and a layer of pressure-release material between said arc and said last-defined means.

3. A transducer comprising a wound cylindrical arc of magnetostrictive material, said arc being substantially less than 180, and a return path comprising a stack of laminations of linx-conducting material spanning the arcuate limits of said magnetostrictive material, said return path including a permanent magnet.

4. A transducer comprising an elongated generally cylindrical arc of magnetostrictive material of less than 180, ux-conducting means extending chordally of the arcuate limits of said magnetostrictive material, means for magnetizing the path defined by said arc and by said chordally extending means, and a signal winding coupled to said path.

5. A transducer comprising an elongated generally cylindrical arc of laminated magnetostrictive materia-l of less than 180, a magnetic return path connecting the limits of said arc and including a permanent magnet, and a signal winding linked to a portion of the path defined by said arc and said chord.

6. A transducer comprising an elongated generally cylindrical arc of laminated magnetostrictive material, said arc being less than 180, a return path continuously connecting limits of said arc and extending chordally of said arc, said return path including a stack of laminations of flux-conducting material exhibiting relatively low magnetostrictive eect, and means for magnetizing the magnetic path defined by said magnetostrictive and relatively non-magnetostrictive materials.

7. A transducer according to claim 6, in which said magnetizing means is a permanently magnetized ferrite block electively coextensive with the longitudinal axis of said arc.

8. A transducer comprising an elongated generally cylindrical are of laminated magnetostrictive material of less than 180, a signal winding coupled to said arc, the respective turns of said winding extending longitudinally of said arc, and a return path connecting the limits of said arc and extending chordally of said arc, said return path including a permanent magnet and tluxconducting material exhibiting relatively low magnetostrictive properties.

9. A transducer comprising a iiat non-magnetic back plate, substantially flat magnetic-ilux-conducting means bonded to said back plate and extending along an elongated axis, a generally cylindrical arc of less than 180 of ,magnetostrictive material secured at its arcuate limits to said flux-conducting means so that said flux-conducting means defines a chordally extending return path for flux in said arc, means for magnetizing said path, and a signal winding linked to said path.

10. A transducer comprising an elongated back plate of non-magnetic material, two substantially parallel elongated stacks of laminations of ilux-conducting means bonded to one side of said plate, permanently magnetized means connecting said stacks and substantially coextensive with the longitudinal axis of said transducer, a cylindrically arcuate ,magnetostrictive member connected at its arcuate ends with -said respective stacks, and a Winding linkedto said arcuate member.

1:1. A `transducer'according'to claim 10, yin which `the volume of said transducer Awithin said arc is lled fwith a potting of hard plastic material.

`12. A transducer according to `claim 10, Ain which the faces of said stacks away from `said :plate havelselongatcd grooves facing upwardly therefrom and receiving the arcuate limits of said magnetostrictive member.

13. A transducer according toclaim 10, and including a boot of rubber-like material `completely encasing said back plate and 4said arcuate portion and including elongated ianges projecting outwardly of the arcuate limits of said transducer and extending .coextensively :with the longitudinal axisrof said transducer.

1.4. A `transducer comprising :.a flux-.conducting path defined by `an arcuate portion Vand a chordallysextending portion Vconnecting the limits of `said arcuate portion, said chordally extending portion `beingglessathan `twice Vthe radius of said arc, one of saidportions being of magnetostrictive material and 4the other of said portions ,being of ux-conducting material exhibiting relatively little magnetostrictive effect, means `for polarizing said path, and a signal winding linked to said path.

15. A transducer array comprising a plurality ,oft elongated transducers of segmental cross-section, the arcuate extent of said cross-,section `being suhstantiallyless than 180, said `transducers being oriented inrelatve close side-by-side relation with .-theirelonga-tedaxes parallel to each other and with their cylindrically `insulate faces directed predominantly in the same directiomwhcrcby maximum responsegin said direction maybe `realized- 16. AA transducer armi/.comprising "a plurality otelec-` t-roacoustic transducer `elements of rsegrrnsntal `cross-sec: tion `and :haring predominant elongated 4axes Parallel t0 each other, p each of `said 1.transducer elements thai/ing i11- tcgral `-yieldal11le mounting Harness extending `outwardly of the arcuate limitsof each saidutransduser, saidfangcs 'being :longitudinally cccxtensive :with leach said transducer clement, and .means securing adjacent imitating flanges of adiacent transducers together,

..17 .An array -accc s ne to claim 1.6, and `including means supporting As 1. mounting `tanscs css -tally the same plane, with; s arcuate zfsccsf .ssidwtransduccfs directed in the same gcscralslrsction.

" snstiscerscc., rig t0` claim .15mm-including e, s supported adiscsnt the chsrslally ,entsantransdsccrelcmsntss cer acccrsinstc clairs `.1@ sndinclusiing compliant vins means hshistirths chcrclally man@ isaifaccsfofgsaid tran csr .clcrsssts- .2.Q A transducer, comprising e cylindrical .atc {ncrticn .of magneticdluxccnductngrmafcrial of srcastc tent dass han 18D?, @a Chard `portion `cf i mssnsticrsxconducting msfcrsltspannng said arc and rigidly ccnnscted to .the srcuatcglimits thereof, cris cf ,said pcrtcss being magnctcstrictivc and fhcux Path dcncd Vbysaid portions bsixrgnclaracd, and s signal wisdinsplnlccd .to onset saidrsrticns- `inferences .Cited in thc tile cf this lpatent UNITED ,STATES PATENTS "2g-391,678 Bundy Dec. v25, 1945 

